I got it working! For future people coming to this looking for an answer here are my config files:

NodeBB config.json:

{
    "url": "http://127.0.0.1/forum",
    "port": "3000",
    "secret": "6a6e220f-ecf3-40f9-8832-55e429184458",
    "bind_address": "0.0.0.0",
    "database": "mongo",
    "mongo": {
        "host": "127.0.0.1",
        "port": "27017",
        "username": "matt",
        "password": "20matt02",
        "database": "nodebb"
    },
    "bcrypt_rounds": 12,
    "use_port": false,
    "relative_path": "/forum"
}

and Apache2 000-default.conf:

<VirtualHost *:80>
    # The ServerName directive sets the request scheme, hostname and port that
    # the server uses to identify itself. This is used when creating
    # redirection URLs. In the context of virtual hosts, the ServerName
    # specifies what hostname must appear in the request's Host: header to
    # match this virtual host. For the default virtual host (this file) this
    # value is not decisive as it is used as a last resort host regardless.
    # However, you must set it for any further virtual host explicitly.
    #ServerName www.example.com
    ServerName 127.0.0.1/forum

    ServerAdmin webmaster@localhost
    DocumentRoot /var/www/html

    # Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
    # error, crit, alert, emerg.
    # It is also possible to configure the loglevel for particular
    # modules, e.g.
    #LogLevel info ssl:warn

    ErrorLog ${APACHE_LOG_DIR}/error.log
    CustomLog ${APACHE_LOG_DIR}/access.log combined

    # For most configuration files from conf-available/, which are
    # enabled or disabled at a global level, it is possible to
    # include a line for only one particular virtual host. For example the
    # following line enables the CGI configuration for this host only
    # after it has been globally disabled with "a2disconf".
    #Include conf-available/serve-cgi-bin.conf
    
    
    ProxyRequests off
    
    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>

    ProxyPass /forum http://127.0.0.1:3000/forum
    ProxyPassReverse /forum http://127.0.0.1:3000/forum

</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet

@Bilou said:

Try to add

ServerName 127.0.0.1/forum

in your 000-default.conf

And change your relative_path by "/" in config.json

Don't forget to change all the 4567 port by 3000.

Can you give me an example with the correct usage. I forgot to mention that none of the styles are showing up(The directory goes to like /forum/plugins/nodebb-plugin-markdown/styles/railscasts.css).

@jbob Thank you for the example, but it was giving me an error on startup(Apache) that said, "Job for apache2.service failed. See "systemctl status apache2.service" and "journalctl -xe" for details." and I checked them, but it did not give me any details.

So I am trying to get my NodeBB working with Apache2 with this URL: "http://127.0.0.1/forum" But when ever I try it it says, "/ Not Found" Here is my config.json:

{
    "url": "http://127.0.0.1/forum",
    "port": "3000",
    "secret": "6a6e220f-ecf3-40f9-8832-55e429184458",
    "bind_address": "0.0.0.0",
    "database": "mongo",
    "mongo": {
        "host": "127.0.0.1",
        "port": "27017",
        "username": "matt",
        "password": "20matt02",
        "database": "nodebb"
    },
    "bcrypt_rounds": 12,
    "use_port": false,
    "relative_path": "/forum/"
}

And my 000-default.conf:

<VirtualHost *:80>
	# The ServerName directive sets the request scheme, hostname and port that
	# the server uses to identify itself. This is used when creating
	# redirection URLs. In the context of virtual hosts, the ServerName
	# specifies what hostname must appear in the request's Host: header to
	# match this virtual host. For the default virtual host (this file) this
	# value is not decisive as it is used as a last resort host regardless.
	# However, you must set it for any further virtual host explicitly.
	#ServerName www.example.com

	ServerAdmin webmaster@localhost
	DocumentRoot /var/www/html

	# Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
	# error, crit, alert, emerg.
	# It is also possible to configure the loglevel for particular
	# modules, e.g.
	#LogLevel info ssl:warn

	ErrorLog ${APACHE_LOG_DIR}/error.log
	CustomLog ${APACHE_LOG_DIR}/access.log combined

	# For most configuration files from conf-available/, which are
	# enabled or disabled at a global level, it is possible to
	# include a line for only one particular virtual host. For example the
	# following line enables the CGI configuration for this host only
	# after it has been globally disabled with "a2disconf".
	#Include conf-available/serve-cgi-bin.conf
	
	
	ProxyRequests off
	
	<Proxy *>
	    Order deny,allow
	    Allow from all
	</Proxy>
	ProxyPass /socket.io/1/websocket ws://127.0.0.1:4567/socket.io/1/websocket
	ProxyPassReverse /socket.io/1/websocket ws://127.0.0.1:4567/socket.io/1/websocket

	ProxyPass /socket.io/ http://127.0.0.1:4567/socket.io/
	ProxyPassReverse /socket.io/ http://127.0.0.1:4567/socket.io/

	ProxyPass /forum http://127.0.0.1:3000
	ProxyPassReverse /forum http://127.0.0.1:3000

</VirtualHost>

# vim: syntax=apache ts=4 sw=4 sts=4 sr noet